REPOET ON THE SCHIZOPODA. 159 



The Antennulce (figs. 1-5). — These limbs, constituting in the Nauplius and Meta- 

 nauplius stages simple, non-articulate stems, exhibit each of them (fig. 1) in the earliest 

 Calyptopis stage described above, and apparently corresponding to the second Calyptopis 

 stage of Nyctiphanes, a slender non-articulate peduncle, bearing at the apex two very 

 small, uniarticulate flagella, the outer a little longer than the inner, and provided with a 

 pair of slender bristles and two sensory appendages. 



In the following (last) Calyptopis stage, these limbs (fig. 2) are much more fuUy 

 developed, the peduncle being rather strong, and di^dded into three distinctly defined 

 joints, of which the basal is by far the largest, and projects at the end exteriorly as a- 

 strong spine, denticulate at the inner edge, and reaching almost to the end of the 

 peduncle. The second joint is quite short, and bears at the inner edge two strong 

 ciliate setse. The last joint is almost twice as long, and has a single bristle internally. 

 The flageUa do not exhibit any essential difference from those in the preceding stage. 



In the FurcHia stages the number of bristles along the inner edge of the peduncle 

 has become somewhat augmented, and the two flagella have slightly increased in length, 

 though still uniarticulate. In the last of these stages (see fig. 3) the long apical bristles 

 of the flagella are lost, and the two sensory appendages of the flagellum, arising originall)- 

 from the tip, are now aflixed to a ledge-like projection of the inner edge, near the base. 



In the Cyrtopia stages the jjeduncle (fig. 4) has a somewhat greater similarity to 

 that of the adult animal, the spine springing from the basal joint being somewhat 

 reduced in size, and both the flagella considerably elongated and divided into a number 

 of distinctly defined articulations. 



But not tili the last stage described above — the first post-larval stage — do the 

 antennulae (fig. 5) assume their definitive form, difi'ering only from those of the adult 

 animal in the dorsal leaflet of the basal joint being still but sHghtly indicated, and in 

 the flagella having not yet attained their fuU length. 



The AntenncB (figs. 6-8). — The structure of these limbs is much the same throughout 

 all the Calyptopis and Furcflia stages. They difi"er widely from those in the adult 

 animal both in form and function, constituting, as they do, very mobile, biramous natatory 

 organs of much the same appearance as that described above in the larvae of Nycti2)hanes, 

 and strongly reminding one of the second pair of antennae in the Calanoid Copepoda. 



In the last Furcilia stage some of the natatory setae are sometimes, however, found 

 to be obliterated (see fig. 6), though in other respects no difference in the sti'ucture of 

 the organs has yet arisen. 



But in the next, or first Cyrtopia stage, these organs (fig. 7) are seen to have 

 suddenly undergone a total alteration alike in structure and function, having lost their 

 great mobility, and assumed a form more in accordance with that of the adult animal. 

 The basal part is shortened and has lost its segmentation, whereas a slender spine has 

 sprung from the end externally, representing the basal spine of the adult animal. Of 



